The line between the conscious and unconscious mind has always been hard to draw. How do you determine if someone is still alive or thinking if they can’t move, speak, or blink? In fact, about 40% of people originally thought to be unconscious are later found to have some level of consciousness.

In the past, scientists thought they could tell simply by looking at patients’ brains through electroencephalography (EEG). The device measures the electrical activity in the brain. Unfortunately, this idea wasn’t as accurate as they hoped. When they hooked one up to a slab of Jell-O, they discovered that it registered similar brainwaves (specifically, alpha waves) to a living, conscious adult. Needless to say, neuroscientists know that EEG alone isn’t enough to tell a thinking human being from a delicious dessert.

EEG alone can't tell if a person is alive or conscious.

Now, scientists believe they’ve hit on a new combination of tools to better delineate who’s aware and who’s not. Published in Science Translational Medicine, researchers at the University of Milan used magnetic stimulation combined with EEG to create a scale of consciousness. The stimulation of brain cells was achieved by putting a large magnet near a patient’s head, a strategy called transcranial magnetic stimulation (TMS). (This technique has also been used—somewhat controversially—to boost brainpower.) This resulting brain activity, which the researchers called an “echo,” was then picked up by an EEG. This data was translated into a numerical score (the perturbational complexity index, or PCI) between 0 and 1, with higher numbers—about 0.6 and above—representing consciousness in healthy individuals.

Here’s Kelly Servick, writing for AAAS’s ScienceNow:

Then the researchers tested the index with 20 people who had suffered different types of brain damage. Those who were believed to be in a vegetative state—awake but completely unconscious—got very low scores (between 0.19 to 0.31). Subjects who had emerged from a coma had varying degrees of awareness and intermediate scores. Two of the patients had a condition known as locked-in syndrome: Their cognitive abilities were normal, but they were unable to move. These patients, who could communicate by shifting their eyes, received PCI scores of 0.51 and 0.62—as high as the waking, healthy subjects. Without requiring any active participation from subjects, this index can reliably place them on a continuum between conscious and unconscious, the team concludes.

Researchers hope the technique will lead toward a more reliable way to determine consciousness. Or at least tell humans from Jell-O.

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